1. Field of the Invention
The present invention relates to an optical transmitter, in particular, the invention relates to an optical transmitter that installed within an optical data link for the optical communication and installs a semiconductor laser diode digitally controlled in the bias and modulation current supplied thereto.
2. Related Prior Art
Various techniques and circuits have been disclosed to control the optical output from the laser diode in the magnitude and the extinction ratio thereof. The United States Patent, U.S. Pat. No. 7,106,768, has disclosed a method to control the LD, where the controller reads from the memory a pair of data, one for the bias current and the other for the modulation current, and sets both currents based on thus read data.
The memory of the transmitter disclosed in the prior art above stores a set of combinations of the currents to obtain a desired optical power and an extinction ratio for the LD. Such combinations of the currents strongly depends on individual devices, accordingly, it is necessary to measure optimal combinations of the currents to maintain the desired optical power and the extinction ratio as varying a temperature of the LD and to store such combinations in the memory at the initial operation of the transmitter. Thus, a large size of the memory is necessary to enhance the preciseness of the control of the LD, which enlarges the circuit size and raises the cost of the transmitter.
The present invention, considering the subjects mentioned above, is to provide an optical transmitter where the size of the data stored in the memory may be saved and accordingly the physical size thereof may be reduced.